Mix together salami and cornichons. Divide cheese among 4 slices of bread. Top with salami and cornichon mixture. If desired, spread remaining bread with mustard. Place remaining bread on top to create sandwiches.

Heat a panini or grill pan over medium heat. Spray with olive oil or cooking spray. Place sandwiches in pan, then press with a panini press or heavy cast iron skillet. After 3-4 minutes, flip. Cook until all cheese is melted and bread is toasted. Serve.